Refactor code.

Source/MQTTnet/Client/MqttClient.cs

@@ -92,8 +92,6 @@ namespace MQTTnet.Client
             remove => _inspectPacketEvent.RemoveHandler(value);
         }
         
-        [Obsolete(
-            "This property will be removed in the future. Checking for a working connection should be done via calling _PinAsync_. Also other successful traffic can be used to indicate connection status.")]
         public bool IsConnected => (MqttClientConnectionStatus)_connectionStatus == MqttClientConnectionStatus.Connected;
 
         public MqttClientOptions Options { get; private set; }

Source/MQTTnet/Internal/AsyncLock.cs

@@ -10,8 +10,8 @@ namespace MQTTnet.Internal
 {
     public sealed class AsyncLock : IDisposable
     {
-        readonly object _syncRoot = new object();
         readonly Task<IDisposable> _releaser;
+        readonly object _syncRoot = new object();
 
         SemaphoreSlim _semaphore = new SemaphoreSlim(1, 1);
 
@@ -20,6 +20,15 @@ namespace MQTTnet.Internal
             _releaser = Task.FromResult((IDisposable)new Releaser(this));
         }
 
+        public void Dispose()
+        {
+            lock (_syncRoot)
+            {
+                _semaphore?.Dispose();
+                _semaphore = null;
+            }
+        }
+
         public Task<IDisposable> WaitAsync(CancellationToken cancellationToken)
         {
             Task task;
@@ -45,22 +54,10 @@ namespace MQTTnet.Internal
             }
 
             // Wait for the _WaitAsync_ method and return the releaser afterwards.
-            return task.ContinueWith(
+            return task.ContinueWith((_, state) => (IDisposable)state, _releaser.Result, cancellationToken, TaskContinuationOptions.ExecuteSynchronously, TaskScheduler.Default);
-                (_, state) => (IDisposable)state, 
-                _releaser.Result, 
-                cancellationToken, TaskContinuationOptions.ExecuteSynchronously, TaskScheduler.Default);
         }
 
-        public void Dispose()
+        void Release()
-        {
-            lock (_syncRoot)
-            {
-                _semaphore?.Dispose();
-                _semaphore = null;
-            }
-        }
-
-        internal void Release()
         {
             lock (_syncRoot)
             {

Source/MQTTnet/Server/Internal/MqttClientSessionsManager.cs

@@ -23,6 +23,8 @@ namespace MQTTnet.Server
     {
         readonly Dictionary<string, MqttClient> _clients = new Dictionary<string, MqttClient>(4096);
 
+        readonly AsyncLock _createConnectionSyncRoot = new AsyncLock();
+
         readonly MqttServerEventContainer _eventContainer;
         readonly MqttNetSourceLogger _logger;
         readonly MqttServerOptions _options;
@@ -38,8 +40,6 @@ namespace MQTTnet.Server
         readonly object _sessionsManagementLock = new object();
         readonly HashSet<MqttSession> _subscriberSessions = new HashSet<MqttSession>();
 
-        readonly SemaphoreSlim _createConnectionSyncRoot = new SemaphoreSlim(1, 1);
-        
         public MqttClientSessionsManager(
             MqttServerOptions options,
             MqttRetainedMessagesManager retainedMessagesManager,
@@ -441,6 +441,11 @@ namespace MQTTnet.Server
             return GetClientSession(clientId).SubscriptionsManager.Unsubscribe(fakeUnsubscribePacket, CancellationToken.None);
         }
 
+        MqttClient CreateClient(MqttConnectPacket connectPacket, IMqttChannelAdapter channelAdapter, MqttSession session)
+        {
+            return new MqttClient(connectPacket, channelAdapter, session, _options, _eventContainer, this, _rootLogger);
+        }
+
         async Task<MqttClient> CreateClientConnection(
             MqttConnectPacket connectPacket,
             MqttConnAckPacket connAckPacket,
@@ -474,8 +479,7 @@ namespace MQTTnet.Server
                 sessionShouldPersist = !connectPacket.CleanSession;
             }
 
-            await _createConnectionSyncRoot.WaitAsync(CancellationToken.None).ConfigureAwait(false);
+            using (await _createConnectionSyncRoot.WaitAsync(CancellationToken.None).ConfigureAwait(false))
-            try
             {
                 MqttSession session;
                 lock (_sessionsManagementLock)
@@ -528,24 +532,19 @@ namespace MQTTnet.Server
 
                     if (_eventContainer.ClientConnectedEvent.HasHandlers)
                     {
-                        var eventArgs = new ClientDisconnectedEventArgs(existingClient.Id, MqttClientDisconnectType.Takeover, existingClient.Endpoint, existingClient.Session.Items);
+                        var eventArgs = new ClientDisconnectedEventArgs(
+                            existingClient.Id,
+                            MqttClientDisconnectType.Takeover,
+                            existingClient.Endpoint,
+                            existingClient.Session.Items);
                         await _eventContainer.ClientDisconnectedEvent.InvokeAsync(eventArgs).ConfigureAwait(false);
                     }
                 }
             }
-            finally
-            {
-                _createConnectionSyncRoot.Release();
-            }
 
             return client;
         }
 
-        MqttClient CreateClient(MqttConnectPacket connectPacket, IMqttChannelAdapter channelAdapter, MqttSession session)
-        {
-            return new MqttClient(connectPacket, channelAdapter, session, _options, _eventContainer, this, _rootLogger);
-        }
-
         MqttSession CreateSession(string clientId, IDictionary sessionItems, bool isPersistent)
         {
             _logger.Verbose("Created new session for client '{0}'.", clientId);